XG is the XG blood group antigen, and is at the pseudoautosomal boundary on the short (p) arm of chromosome X. The three 5' exons reside in the pseudoautosomal region and the remaining exons within the X-specific end. A truncated copy of this gene is found on the Y chromosome at the pseudoautosomal boundary. It is transcribed, but not expected to make a Y-chromosome specific gene product. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. Recombinant human XG protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.